This invention pertains to a monitor, preferably a cathode ray tube (CRT) monitor and, more particularly, to a CRT monitor that provides a means for image manipulation.
Conventional monitor, for example CRT monitors, have some geometry distortion dependent upon the input display signals and magnetic fields in the vicinity of the monitor. Conventional monitor have an adjustment function using modulation circuits and coils. Such an arrangement is expensive in that it incurs additional hardware and manufacturing costs.
What is needed is a convenient and efficient way to adjust for image distortion in a monitor.
The above and other objectives are achieved by monitor, preferably a CRT monitor, according to the present invention that includes a display screen for displaying an image, a frame memory for storing one or more frames of video display data for display by the display screen, and a clock control means for varying the timing at which the display data are read out from the frame memory to the display screen to manipulate the image displayed on the display screen.
In the preferred embodiment, the display screen includes a horizontal scanning frequency signal generator that generates a horizontal scanning signal including a horizontal sync signal and the clock control means produces a clock signal corresponding to a predetermined multiple of the horizontal scanning frequency. The clock signal has a variable delay with respect to the horizontal sync signal. The variable delay can be before the horizontal sync signal, after the horizontal sync signal, or both. Alternatively, or in addition the clock control means dynamically adjusts the periods between clock signal pulses. Further, the periods between clock pulses at the beginning of a horizontal display line on the display screen can be longer than the periods between the clock pulses at the end of the horizontal display line on the display screen or, alternatively, the periods between clock pulses in the middle of a horizontal display line on the display screen are shorter than the periods between the clock pulses at the beginning and end of the horizontal display line on the display screen.
The invention also includes a method for manipulating an image displayed on a monitor, preferably a CRT monitor, comprising the steps of displaying an image on a display screen, storing one or more frames of video display data for display by the display screen in a frame memory, and varying the timing at which the display data are read out from the frame memory to the display screen to manipulate the image displayed on the display screen. The method of the preferred embodiment further includes the steps of generating a horizontal scanning signal including a horizontal sync signal and producing a clock signal corresponding to a predetermined multiple of the horizontal scanning frequency. The clock signal has a variable delay with respect to the horizontal sync signal and/or a variable delay both before the horizontal sync signal and after the horizontal sync signal. Additionally or alternatively, the periods between clock signal pulses are dynamically adjusted. This includes making the periods between clock pulses at the beginning of a horizontal display line on the display screen longer than the periods between the clock pulses at the end of the horizontal display line on the display screen or making the periods between clock pulses in the middle of a horizontal display line on the display screen shorter than the periods between the clock pulses at the beginning and end of the horizontal display line on the display screen.
The foregoing and other objectives, features and advantages of the invention will be more readily understood upon consideration of the following detailed description of certain preferred embodiments of the invention, taken in conjunction with the accompanying drawings.